1. Field of the Invention
The present invention relates to a semiconductor laser element, and in particular to a semiconductor laser element which can be used as a light source in an information processing device.
2. Description of the Related Art
The personal computers have penetrated into offices and homes, and progressed so that the processing speeds of the current personal computers are comparable to the supercomputers of tens of years past. In particular, the increase in the processing speeds of the CPUs is remarkable, and the clock frequencies of some of the currently available CPUs exceed 3 GHz. It is considered that the clock frequencies of CPUs can be increased to about 10 GHz by using only the currently known techniques.
However, even when the processing speeds of the CPUs per se are increased, the substantial processing speeds of computers do not increase unless the data transfer rates between each CPU and other elements, such as memories and LSIs (large-scale integrated circuits) for image processing, increase. Therefore, an attempt to increase the data transfer rate by connecting a CPU and LSIs and memories with optical wiring has been made. For example, Osamu Ibaraki et al. (“Low-Cost Opto-Electronic Packaging Technology for High-Speed IT Appliances,” Osamu Ibaragi, et al., Technical Research Report, Vol. 102, No. 284, pp. 37-42, IEICE, 2002) disclose a technique in which LSIs, driver/receiver ICs, submount substrates, surface-emitting semiconductor lasers, and photodetectors are three-dimensionally mounted, and through-holes are formed in the semiconductor lasers and the photodetectors, and arranged in proximity to optical waveguides so that the semiconductor lasers and the photodetectors are optically coupled.
The light sources used for optical transfer between LSIs are required to be arranged in proximity to the LSIs. Therefore, there is concern about the influence of the heat generated by the LSIs. For example, in the case of the Pentium, which is currently widely used as a CPU in a personal computer, it is said that the surface temperature of the package base reaches 70° C. during use. (Pentium is a registered trademark of Intel Corporation.) Therefore, the light sources used for optical transfer between LSIs are required to stably operate in a high temperature environment, and maintain their performance regardless of the ambient temperature.
Currently, the surface-emitting semiconductor lasers are the most promising device as light sources used for optical wiring connecting LSIs. However, the surface-emitting semiconductor lasers have structural constraints which increase resistance. Therefore, the surface-emitting semiconductor lasers per se generate great heat, and raise the ambient temperature, so that the optical output characteristics deteriorate. If such surface-emitting semiconductor lasers are arranged in proximity to the LSIs, the driving currents can vary with the ambient temperature. Further, the temperature rise can stop the oscillation of the semiconductor lasers, and make transmission of optical signals impossible.
On the other hand, use of the edge-emitting semiconductor lasers as light sources for optical wiring is currently being considered. Since the semiconductor lasers in the 0.6, 1.3, and 1.55 μm bands do not have satisfactory temperature characteristics, the 0.8 μm-band semiconductor lasers are considered as potential devices. However, the temperature characteristics of the 0.8 μm-band semiconductor lasers do not indicate that the 0.8 μm-band semiconductor lasers are suitable for use immediately under LSIs. Therefore, further improvement in the temperature characteristics of the 0.8 μm-band semiconductor lasers is required.